You need to get the appropriate PowerPC cross-compiler setup for the S1 box.
It's been a while since I last knocked one up but it is not that difficult to do and there is absolutely no reason to use some ancient Linux (in fact it will just make your life a LOT harder). Recent Debian/Ubuntu etc. will be just fine to 'host' the cross-compiler
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You will also need the kernel headers for the 2.5.* image on the UK TiVo, if you can't find them I am sure I have them somewhere on my server.